Temperature is one of the most basic physical parameters influencing physical chemistry process and biological metabolism process. Thus, no matter in scientific research or in daily life, temperature detection is necessary, and temperature sensors accounts for 75-80% of worldwide market of sensors (Review of Scientific Instruments 2000, 71, 2959-2978). Temperature detection in different conditions or different research objects requires different temperature sensors. Along with the rapid development of disciplines and technologies such as molecular biology, proteomics, medical science and scientific instruments, multiple research fields have got in micro-dynamic detection process, for example the research of biological metabolism process and disease has extended to the process of molecule changes in biological cells (Nature medicine 2003, 9, 149-150). Such development has presented new challenge to temperature detection: real-time and remote detection of temperature and temperature distribution in a microenvironment. Traditional sensors detecting temperature by local contact, for example temperature sensor based on volume changes through thermal expansion and contraction of a substance, and thermocouple temperature indicator designed according to thermoelectric effect (Seebeck effect), can't fulfill the need of the development of these disciplines. In this aspect, fluorescent molecular or nano temperature sensors which have advantages such as ultrahigh sensitivity, extremely fast response speed, extremely high spatial resolution and safe remote detection, have attracted great attention (Chemical Society Reviews 2013, 42, 7834-7869).
Theoretically, the fluorescence of all fluorescent compounds is related to temperature. This is because, on the one hand, temperature variation would bring the changes in the electronic energy level and electronic vibration level distribution of atoms or molecules, which thus would change the fluorescent property; on the other hand, temperature variation would bring change in the volume of compound, which would influence the interactions between atoms or between molecules and then change the fluorescent property. However, fluorescent compounds used as temperature probes are less because the compound serving as the temperature probe should satisfy the properties such as high sensitivity, good stability and reversibility (Chemical Society Reviews 2013, 42, 7834-7869). Nowadays, the reported thermo-sensitive fluorescent materials include macromolecular fluorescent compounds, small organic molecule fluorescent compounds, organometallic complexes, quantum dots, organic or inorganic nano materials, etc. (Chemical Society Reviews 2013, 42, 7834-7869). Some of fluorescent temperature probes have been used in intracellular temperature detection and imaging study, for example macromolecule compound 1 can be used in intracellular temperature imaging (Nature communications 2012, 3, 705) (FIG. 1).
Compared with inorganic and macromolecule fluorescent materials, the properties of small molecular organic fluorescent materials are relatively easy to be controlled owing to the following characteristics: (1) compounds with different optical properties can be easily obtained by structural modification; (2) material properties can be modified by oriented assembly in molecular level easily; (3) functional molecular structures can be changed on purpose to combine and integrate multiple functions.
Besides, compared to temperature fluorescent probes of metallic quantum dots and metallic complexes, the temperature fluorescent probes of small molecular organic compounds are provided with less toxicity. But so far, fluorescent probes with high sensitivity and wide temperature range are metallic complex, quantum dot and organic polymer (Chemical Society Reviews 2013, 42, 7834-7869). Small molecular organic compounds that can be used as temperature probes are less, and most of them are molecular thermometers which are used in solutions and related to not only temperature but also solution polarity and pH value. For example, the fluorescence of compound 2 (FIG. 2) is related to not only temperature but also solution polarity, and it can only be used to detect temperature of solution with certain polarity. Thus, the temperature response of compound 2 was conducted in a polar solution of 2-methoxyethyl ether (FIG. 2) (Angew. Chem. Int. Ed. 2011, 50, 8072-8076). The application of such probe is limited, because the ideal temperature probe should be related to only temperature but not to other environmental factors. Environmental-responsive solid reversible fluorescent change has a more comprehensive application, but solid fluorescent compounds with reversible change by thermal stimulus are fairly less. As shown in FIG. 3, a fluorescence intensity of compound 3 (Nat Mater 2005, 4, 685-687), and the dual-color fluorescence of compound 4 (Chemical Communications 2012, 48, 10895-10897) display reversible change along with temperature. The solid-state fluorescence of organic compounds is related to not only molecular structures but also molecular stacking modes. The sensitive thermo-response of compounds 3 and 4 proves to be originated from the thermo-stimuli reversible change in molecular stacking modes.
The present inventor has disclosed penta-substituted tetrahydropyrimidines in CN201110129857.X, which have an aggregation-induced emission effect and can be used in organic electro-luminescence or photo-luminescence devices or chemical and biological fluorescent sensors and probes.